This invention relates to alkylation and transalkylation processes and catalysts for use therein. The invention is particularly concerned with catalysts having an initial content of water sufficiently high to decrease catalyst deactivation by inhibiting reactant decomposition during the start-up of such processes, thereby significantly increasing the life of the catalysts.
In the past it has been common practice to alkylate aromatic molecules such as benzene, toluene and xylene with ethylene, propylene and other olefins using acidic homogeneous Friedel-Crafts type catalysts such as aluminum halides or heterogeneous acidic silica-alumina catalysts. Such processes have several disadvantages including corrosion problem caused by some of the catalysts and difficulty in controlling the product distribution obtained from the alkylation reactions. Often, the desired product is the monoalkylate rather than the di- or trialkylate. In an effort to avoid a large production of di- and trialkylate products and to extend catalyst life, it is conventional practice to use a large excess of the aromatic compound.
To avoid some of the problems associated with earlier commercial alkylation processes, solid zeolite-containing catalysts have been used in recent years to promote the alkylation of aromatic compounds with olefins and other alkylating agents, especially the alkylation of benzene with ethylene. Such zeolite-containing catalysts are normally prepared by combining a zeolite with a refractory oxide binder or precursor thereof, mulling and extruding the mixture, drying the extrudates and then calcining the dried extrudates at high temperatures to provide the extrudates with the strength required to withstand commercial operations. Naturally occurring and synthetic zeolites typically contain a relatively large concentration of sodium ions and are therefore not catalytically active. Thus, before a zeolite is mixed with the refractory oxide component or precursor thereof in the manufacturing of a zeolite-based catalyst, the zeolite is normally subjected to ion exchange, typically with ammonium ions, to reduce its sodium concentration as low as practically possible and increase its catalytic activity. However, since ammonia is known to poison the acid sites of the zeolite, it is common practice to carry out the calcination of the dried extrudates at such temperatures that substantially all of the ammonium ions in the catalyst are decomposed into hydrogen ions and ammonia which is driven out of the catalyst as a gas. The use of such calcination temperatures also drives off substantially all of the water present and typically results in a substantially dry catalyst.
Normally, zeolite-based alkylation catalysts prepared as described above are used in fixed bed reactors through which the reactants are continuously passed. Although such fixed bed processes using zeolite-containing catalysts have advantages over earlier commercial processes, the life and deactivation rate of the catalysts, especially when used to produce ethylbenzene by reacting ethylene with benzene, have been observed in pilot plant studies to vary from one catalyst to another with the life of some of the catalysts being so low that commercial processes using such catalysts would be uneconomical.
Accordingly, there is a need for zeolite-containing catalysts that do not readily deactivate when used to catalyze alkylation and transalkylation reactions, and therefore consistently maintain a relatively long life.